250
AT90PWM216/316 [DATASHEET]
7710H–AVR–07/2013
Capacitors connected to the RESET pin must be disconnected when using debugWire.
All external reset sources must be disconnected.
22.4
Software Break Points
debugWIRE supports Program memory Break Points by the AVR Break instruction. Setting a Break Point in AVR
Studio
will insert a BREAK instruction in the Program memory. The instruction replaced by the BREAK instruction
will be stored. When program execution is continued, the stored instruction will be executed before continuing from
the Program memory. A break can be inserted manually by putting the BREAK instruction in the program.
The Flash must be re-programmed each time a Break Point is changed. This is automatically handled by AVR Stu-
dio through the debugWIRE interface. The use of Break Points will therefore reduce the Flash Data retention.
Devices used for debugging purposes should not be shipped to end customers.
22.5
Limitations of debugWIRE
The debugWIRE communication pin (dW) is physically located on the same pin as External Reset (RESET). An
External Reset source is therefore not supported when the debugWIRE is enabled.
The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e., when the program in
the CPU is running. When the CPU is stopped, care must be taken while accessing some of the I/O Registers via
the debugger (AVR Studio).
A programmed DWEN Fuse enables some parts of the clock system to be running in all sleep modes. This will
increase the power consumption while in sleep. Thus, the DWEN Fuse should be disabled when debugWire is not
used.
22.6
debugWIRE Related Register in I/O Memory
The following section describes the registers used with the debugWire.
22.6.1
debugWire Data Register – DWDR
The DWDR Register provides a communication channel from the running program in the MCU to the debugger.
This register is only accessible by the debugWIRE and can therefore not be used as a general purpose register in
the normal operations.
Bit
76543210
DWDR[7:0]
DWDR
Read/Write
R/W
Initial Value
00000000